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Earth’s extreme life holds hints to Martian past

By Michael Slezak

Home sweet home

(Image: Kathleen Benson)

LIFE has been found hiding in one of the most inhospitable lakes on Earth, one which closely resembles what we think Martian lakes looked like. The finding suggests that we need to look for evidence of life on Mars in a new way.

Extreme environments all over our planet have been probed for life. But most are extreme in just one way&colon; temperature or pH, say. “If the water has a really high temperature and that is the only extreme condition, then the life forms only need to cope with temperature extremes,” says Kathleen Benison at West Virginia University, who made the find with Amber Conner, now at Central Michigan University.

Examining Lake Magic in Western Australia, Benison and Conner found it to be extreme in almost every way. They measured the pH at 1.7 – about the same as stomach acid. The lake can be 10 times as salty as seawater. They also found that levels of dissolved silica, aluminium and sulphur in the lake were as high or higher than in bodies of water famous for high levels of just one of the elements.

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The minerals that fill Lake Magic are consistent with what is thought to be on Mars, as is the water’s acidity. Other good Mars analogues, such as the lakes in the Atacama desert or the Rio Tinto river, are either acidic or salty, but not both.

The pair found two types of life form in the lake&colon; a type of algae that Benison thinks is a new species and a prokaryote – a single-celled organism that lacks a nucleus. They also found possible evidence of a fungi (Astrobiology, doi.org/nq3).

Benison says their work shows life can exist in such harsh acid brines. Even better, it reveals how evidence of life might be found elsewhere – including on Mars.

That’s because all three life forms were found hidden in bubbles inside salt crystals, called fluid inclusions. “Martian rocks may contain minerals that host microorganisms in fluid inclusions and we’d never know it because we are looking in the wrong way,” says Benison.

Martian rocks may host microorganisms and we’d never know it because we look in the wrong way

Current searches for past life on Mars crush rock samples before conducting chemical analyses. Benison believes this destroys the fluid inclusions. A better method would be to examine the rocks optically for signs of the inclusions, she says.

Chris McKay, a NASA astrobiologist, thinks this is an important piece of work for Martian life-hunters. “There has been a tendency for the Mars guys like me to focus on ice, which is understandable since there is a lot of known ice on Mars,” he says. “Salt can stabilise liquid environments in dry and cold conditions and, equally important, it can preserve organic biomarker evidence of life over geological time.”

The next rover visiting Mars – currently known as Mars 2020 – will look for signs of past life with instruments yet to be determined. But there’s a good chance it will use less destructive methods to look for life trapped in a similar way to that seen at Lake Magic, says Abigail Allwood, another NASA astrobiologist. “Rather than analysing an extracted, crushed processed sample, it would put analytical instruments up close to the rock and examine microscale properties in place,” she says.

This article appeared in print under the headline “Extreme life conjures up hints to Martian past”